pkey: change PKey::{RSA,DSA,DH}#params to use nil for missing parameters

The returned Hash from these methods contain 0 in place of a missing
parameter in the key, for example:

	pkey = OpenSSL::PKey.read(OpenSSL::PKey::RSA.new(2048).public_to_pem)
	pp pkey.params
	#=>
	# {"n"=>#<OpenSSL::BN 286934673421[...snip]>,
	#  "e"=>#<OpenSSL::BN 65537>,
	#  "d"=>#<OpenSSL::BN 0>,
	#  "p"=>#<OpenSSL::BN 0>,
	#  "q"=>#<OpenSSL::BN 0>,
	#  "dmp1"=>#<OpenSSL::BN 0>,
	#  "dmq1"=>#<OpenSSL::BN 0>,
	#  "iqmp"=>#<OpenSSL::BN 0>}

Let's use nil instead, which is more appropriate for indicating a
missing value.

lib/openssl/pkey.rb

@@ -42,7 +42,7 @@ def public_key
     # The hash has keys 'p', 'q', 'g', 'pub_key', and 'priv_key'.
     def params
       %w{p q g pub_key priv_key}.map { |name|
-        [name, send(name) || 0.to_bn]
+        [name, send(name)]
       }.to_h
     end
 
@@ -174,7 +174,7 @@ def public_key
     # The hash has keys 'p', 'q', 'g', 'pub_key', and 'priv_key'.
     def params
       %w{p q g pub_key priv_key}.map { |name|
-        [name, send(name) || 0.to_bn]
+        [name, send(name)]
       }.to_h
     end
 
@@ -360,7 +360,7 @@ def public_key
     # The hash has keys 'n', 'e', 'd', 'p', 'q', 'dmp1', 'dmq1', and 'iqmp'.
     def params
       %w{n e d p q dmp1 dmq1 iqmp}.map { |name|
-        [name, send(name) || 0.to_bn]
+        [name, send(name)]
       }.to_h
     end
 

test/openssl/test_pkey_dh.rb

@@ -138,9 +138,9 @@ def test_params
     assert_not_nil dh.g
     assert_equal dh.g, dh.params["g"]
     assert_nil dh.pub_key
-    assert_equal 0, dh.params["pub_key"]
+    assert_nil dh.params["pub_key"]
     assert_nil dh.priv_key
-    assert_equal 0, dh.params["priv_key"]
+    assert_nil dh.params["priv_key"]
 
     dhkey = OpenSSL::PKey.generate_key(dh)
     assert_equal dh.params["p"], dhkey.params["p"]

test/openssl/test_pkey_dsa.rb

@@ -251,7 +251,7 @@ def test_params
     assert_equal key.pub_key, pubkey.pub_key
     assert_equal key.pub_key, pubkey.params["pub_key"]
     assert_nil pubkey.priv_key
-    assert_equal 0, pubkey.params["priv_key"]
+    assert_nil pubkey.params["priv_key"]
   end
 
   def test_dup

test/openssl/test_pkey_rsa.rb

@@ -535,7 +535,7 @@ def test_params
     pubkey = OpenSSL::PKey.read(key.public_to_der)
     [:d, :p, :q, :dmp1, :dmq1, :iqmp].each do |name|
       assert_nil pubkey.send(name)
-      assert_equal 0, pubkey.params[name.to_s]
+      assert_nil pubkey.params[name.to_s]
     end
   end